Category Archives: Coding

Let’s Override Navigation Bar back button click in Xamarin Forms…

So you would like to override the Navigation Bar back button click event in your Xamarin Forms App? 😉 Yeah could be for a Sign up Page, Order Details Page, or any kind of a Page where you want to do some execution or confirmation before the user actually navigates back to the previous page in your app…

It’s BACKWARD navigation time…

Yes we are not talking about forward navigation here, but BACKWARD navigation! where the user clicks on the back button on the Navigation Bar, or the actual Back button in Android phones, where we need to have some validation before the user actually navigates…

Oh hello! Where do you think you’re going? Are you sure you want to go back?

:\

Do you want to save your changes before you go back?

Please complete the empty fields because you go back!

😮

Do you want to go back before you save your changes?

Please confirm you want to cancel your changes and go back…

😛

Blah blah…

Well you know the scenarios… 😉

ummhh… but in Xamarin Forms?

Yeah the question is can we actually implement this behavior in Xamarin Forms?

YES! you can, but…

well yes obviously you can override the OnBackPressed() method in ContentPage control, but…

it works only on Android and only for the physical back button…

not the Navigation Bar back button…

owwhh SNAP!

Yes fellas, if you want to achieve the above behavior in Xamarin Forms, you literally can not do it straight out of the box, because the override-able  OnBackPressed() method in ContentPage only gets fired on Android’s physical (or screen bottom) back button’s click. It does not work for the Navigation Bar’s back button click.

But I did it…

So here’s a sneak preview of the results of my implementation…

  

Now look at that awesomeness.. When the user clicks on the Navigation Bar’s back button, I’m popping up a confirmation dialog.. 🙂

Alright, how did I do this?

So in order to do this we need to drill down to the native level and handle these Navigation Bar back button click. Let me explain further….

Android

So after compilation the Navigation Bar that we call in Xamarin Forms, turns into the Action Bar for Android during run time. So in order to capture the back button click the Action Bar we need to override the OnOptionsItemSelected() in your MainActivity class, which allows us to capture the navigation bar’s back button click. Since Xamarin Forms runs on a single Activity overriding the above event on your parent Activity class is enough to get our job done. 😉

iOS

And for iOS , the Xamarin Forms’s Navigation Bar is mapped to the UINavigationBar in iOS run time. But unfortunately there’s no way to override the back button click on the default back button in the UINavigationBar, the only solution is to replace the default back button with a custom back button and do our necessary event subscriptions with it. We can replace the default back button with our custom back button at the ViewWillAppear() event call of the UIViewController, and set our custom back button to UILeftBarButtonItem property. 😀

Bridging between Native Xamarin and Xamarin Forms?

Yep just by native implementation is not enough since we need to get a call back to our Xamrin Forms PCL or Shared project level right? So for that we shall be using a simple Action event where we subscribe to in our Xamarin Forms code level, and do the necessary execution when the mentioned Action event gets fired from the native project levels. 😉

Simple as that! 😀

Alright! time for coding.. 😀

So first we need to create a Custom ContentPage to be used as our Page in our Xamarin Forms project, where as we could enable or disable the Nav bar Back button event overriding. And we shall name it as the “CoolContentPage” lol, well why not, it is indeed cool! 😉 lol

namespace WhateverYourNamespace
{
    public class CoolContentPage : ContentPage
    {
        /// <summary>
        /// Gets or Sets the Back button click overriden custom action
        /// </summary>
        public Action CustomBackButtonAction { get; set; }

        public static readonly BindableProperty EnableBackButtonOverrideProperty =
               BindableProperty.Create(
               nameof(EnableBackButtonOverride),
               typeof(bool),
               typeof(CoolContentPage),
               false);
			   
        /// <summary>
        /// Gets or Sets Custom Back button overriding state
        /// </summary>
        public bool EnableBackButtonOverride
        {
            get
            {
                return (bool)GetValue(EnableBackButtonOverrideProperty);
            }
            set
            {
                SetValue(EnableBackButtonOverrideProperty, value);
            }
        }
    }
}

 

So there we have created the Action event that we are going to subscribe to in our Xamarin Forms code level and to be invoked from Xamarin native project level.

You can also see that I’m using a bool property to enable or disable the overriding of the Back Button click event, so that we can decide whether to subscribe to the overriding event or not as a page property.

next Xamarin Android stuff…

So as I explained at the beginning we need to override the OnOptionsItemSelected() event in our MainActivity class in order to capture the nav bar back button click in Android for Xamarin Forms.

public override bool OnOptionsItemSelected(IMenuItem item)
{
	// check if the current item id 
	// is equals to the back button id
	if (item.ItemId == 16908332)
	{
	   // retrieve the current xamarin forms page instance
	   var currentpage = (CoolContentPage)
	   Xamarin.Forms.Application.
	   Current.MainPage.Navigation.
	   NavigationStack.LastOrDefault();

	   // check if the page has subscribed to 
	   // the custom back button event
	   if (currentpage?.CustomBackButtonAction != null)
	   {
		 // invoke the Custom back button action
		 currentpage?.CustomBackButtonAction.Invoke();
		 // and disable the default back button action
		 return false;
	   }

	   // if its not subscribed then go ahead 
	   // with the default back button action
	   return base.OnOptionsItemSelected(item);
	}
	else
	{
	   // since its not the back button 
	   //click, pass the event to the base
	   return base.OnOptionsItemSelected(item);
	}
}

public override void OnBackPressed()
{
	// this is not necessary, but in Android user 
	// has both Nav bar back button and
	// physical back button its safe 
	// to cover the both events

	// retrieve the current xamarin forms page instance
	var currentpage = (CoolContentPage)
	Xamarin.Forms.Application.
	Current.MainPage.Navigation.
	NavigationStack.LastOrDefault();

	// check if the page has subscribed to 
	// the custom back button event
	if (currentpage?.CustomBackButtonAction != null)
	{
		currentpage?.CustomBackButtonAction.Invoke();
	}
	else
	{
		base.OnBackPressed();
	}
}

 

phewww… that was some long code snippet yeah! fear not child! let me explain…

So as I mentioned before when the user clicks on anything on the default Android navigation bar the above OnOptionsItemSelected() gets fired, where as we will check the clicked item’s id and check for the back button’s default id. Yes the default back button id is the same 16908332 integer in Xamarin Forms – Android applications.

There we will get an instance of the current Xamarin Forms page in the Navigation stack and look if the page has been subscribed to the Custom Back button click event, if so there we will invoke our CustomBackButtonAction, and disable the default click event. If the page hasn’t subscribed to the Action, then we shall pass the click event to the base allowing the default back stack navigation. 🙂 Simple as that! 😀

Now you may see that I have also overridden the OnBackPressed event as well. This is really not necessary if you don’t want to but as a good practice it’s better to override both Nav bar back button and physical back button click events at the same time.

then Xamarin iOS stuff…

Here comes the iOS implementation where we are going to replace the custom Navigation Bar back button and use our own Custom button for the back button as I explained at the beginning. 😀

Now I know when we are to replace the Back button of iOS, we need to replace it with the same similar looking back button, although its custom. This is not really an easy task, because we need to construct the identical back button from the scratch, including the image, fonts and inset values and so on. I have written a complete blog post about this in one of my previous posts. If you want you could refer to it as for the complete explanation here : Creating an identical Custom Navigation Bar Back Button in Xamarin iOS…

But for the sake of this post, I shall post the whole implementation here, but I shall not drill down to detailed explanation. 🙂 You can always prefer to the original post up there.. 😉

Now keep in mind for iOS you need to override the ViewWillAppear() method in your CoolContentPageRenderer class.

So the below code should be placed inside your CoolContentPageRenderer class…

public override void ViewWillAppear(bool animated)
{
     base.ViewWillAppear(animated);
     
     if (((CoolContentPage)Element).EnableBackButtonOverride)
     {
          SetCustomBackButton();
     }
}

private void SetCustomBackButton()
{
     // Load the Back arrow Image
     var backBtnImage = 
     UIImage.FromBundle("iosbackarrow.png");

     backBtnImage = 
     backBtnImage.ImageWithRenderingMode
     (UIImageRenderingMode.AlwaysTemplate);

     // Create our Button and set Edge 
     // Insets for Title and Image
     var backBtn = new UIButton(UIButtonType.Custom)
     {
          HorizontalAlignment =   
          UIControlContentHorizontalAlignment.Left,
          TitleEdgeInsets = 
          new UIEdgeInsets(11.5f, 15f, 10f, 0f),
          ImageEdgeInsets = 
          new UIEdgeInsets(1f, 8f, 0f, 0f)
     };

     // Set the styling for Title
     // You could set any Text as you wish here
     backBtn.SetTitle("Back", UIControlState.Normal);
     // use the white color in ios back button text
     backBtn.SetTitleColor(UIColor.White,
     UIControlState.Normal); 
     backBtn.SetTitleColor(UIColor.LightGray, 
     UIControlState.Highlighted);
     backBtn.Font = UIFont.FromName("HelveticaNeue",
     (nfloat)17);

     // Set the Image to the button
     backBtn.SetImage(backBtnImage, UIControlState.Normal);

     // Allow the button to Size itself
     backBtn.SizeToFit();

     // Add the Custom Click event you would like to 
     // execute upon the Back button click
     backBtn.TouchDown += (sender, e) =>
     {
          // Whatever your custom back button click handling
          if(((CoolContentPage)Element)?.
          CustomBackButtonAction != null)
          {    
            ((CoolContentPage)Element)?.
               CustomBackButtonAction.Invoke();
          }
     };

     //Set the frame of the button
     backBtn.Frame = new CGRect(
          0,
          0,
          UIScreen.MainScreen.Bounds.Width / 4,
          NavigationController.NavigationBar.Frame.Height);

     // Add our button to a container
     var btnContainer = new UIView(
     new CGRect(0, 0, 
     backBtn.Frame.Width, backBtn.Frame.Height));
     btnContainer.AddSubview(backBtn);

     // A dummy button item to push our custom  back button to
     // the edge of screen (sort of a hack)
     var fixedSpace = 
     new UIBarButtonItem(UIBarButtonSystemItem.FixedSpace)
     {
          Width = -16f
     };
     // wrap our custom back button with a UIBarButtonItem
     var backButtonItem = new UIBarButtonItem("",
     UIBarButtonItemStyle.Plain, null)
     {
          CustomView = backBtn
     };

     // Add it to the ViewController
     NavigationController.TopViewController.
     NavigationItem.LeftBarButtonItems 
     = new[] { fixedSpace, backButtonItem };
}

 

Alright there you have it, now keep in mind you need to attach the iosbackarrow.png image to your Xamarin Forms solution’s iOS project’s Resources folder. 😉

As I mentioned above I will not be getting down to the details of the above implementation, but I will explain the nuts and bolts related to this post.

So if you notice above we are creating a custom button and we are subscribing to the TouchDown event of it, which is where we are going to check if the current page has subscribed to the CustomBackButtonAction event or not and proceed with the custom action or default back stack navigation event… 😀

Simple as that! 😉

How to use it, you asked?

Alright let’s consume this beautiful implementation! 😉

So here I’m using our CoolContentPage as a XAML page in my Xamarin Forms solution.

<WhateverYourNamespace:CoolContentPage 
 xmlns="http://xamarin.com/schemas/2014/forms"
 xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
 xmlns:WhateverYourNamespace=
 "clrnamespace:XFNavBarBackBtnClickOverride;
 assembly=XFNavBarBackBtnClickOverride"
 x:Class="XFNavBarBackBtnClickOverride.Page2"             
 Title="Page 3"
 EnableBackButtonOverride="True"
 BackgroundColor="#00bfff">
  <StackLayout
    Spacing="20"
    Padding="20,10,20,10"
    VerticalOptions="Center"
    HorizontalOptions="Center" >

    <Label Text="This is the cool page, 
	which has the Navigation Bar Back button 
	click overriden. How go ahead and click that Back     
        button! ;)"
           FontSize="20"
           HorizontalTextAlignment="Center"
           TextColor="White"/>
    
  </StackLayout>
</WhateverYourNamespace:CoolContentPage>

 

You can notice that I’m setting the EnableBackButtonOverride=”True” property for enabling the overriding of the nav bar custom back button click.

So here’s in the code behind we are subscribing to the CustomBackButtonAction with our Alert dialog asking a verification if the user is sure that they want to go back.

namespace WhateverYourNamespace
{
    public partial class Page2 : CoolContentPage
    {
        public Page2()
        {
            InitializeComponent();
            
            if (EnableBackButtonOverride)
            {
                this.CustomBackButtonAction = async () =>
                {
                    var result = await this.DisplayAlert(null,
                        "Hey wait now! are you sure " +
                        "you want to go back?",
                        "Yes go back", "Nope");

                    if (result)
                    {
                        await Navigation.PopAsync(true);
                    }
                };
            }
        }
    }
}

 

Pay good attention here where if the user confirms they want to go back, then we will manually Pop the page by calling  Navigation.PopAsync() method. If not the back button click event will be ignored thanks to our custom back button click event overriding implementation. 😀

Now keep in mind, subscribing to the Action can be done in many other different ways, code-behind may not be the best practice if you’re heavy MVVM minded, where as may be you could move the custom Action event subscription to the CoolContentPage’s OnAppearing event or base class. All up to your preferences… 😉

Alright, let’s fire it up!

Oh child, just hit that F5! 😉

  

Look at that beauty! 😀 Well the colors and stylings I added myself though.. 😉

So you may grab the code up in my Github: Xamarin-Playground/XFNavBarBackBtnClickOverride

There you go fellas!

Happy coding and share the love! 😀

Udara Alwis out!

Creating an identical Custom Navigation Bar Back Button in Xamarin iOS…

Now there comes a time when the Developer has to override or customize the Back Button in their Xamarin iOS app. Well I’ve been there, hence let me share my experience…

Now the origin of my experience is that, I wanted to override the Back button click event of my Xamarin iOS, but since there’s no way to actually “override” the back button event, I had to completely get rid of the default back button and implement my own custom back button, but it had to be exactly similar as the original iOS back button…

45ffk

So let me ask you…

Have you ever wanted to override your Navigation Bar Back button in iOS  with Xamarin? or specially override it with an identical or similar looking custom button? may be to gain control of the Back button click event?

Then this post is for you… 😀

tumblr_inline_nl7ryzqono1rkrh6k

Custom, but Similar to the actual Back Button…

Yes that’s right, let me highlight the identical or similar looking custom back button, because it’s pretty simple and straightforward to override or replace the back button, but its a bit of struggle when you want to implement a custom back button which looks identical or similar to the original back button in iOS.

The key…

So the key things to keep in mind is that,

  • We need use an Image with a “Back Arrow” that is similar from look and size of the original back button.
  • Use similar Font size to display the Text
  • Use necessary padding and x/y values to place the Image and Text Title properly

Alright, let’s get into it…

Image with Back Arrow…

Now to find the image for the Back Arrow just google “iphone back button png” or something similar, you could easily find lots, I would recommend to use the icons8 website, which is where I got mine, https://icons8.com/web-app/15157/back

Make sure there’s no padding between the Image pixel space and the borders, in my case the image was 24×41 size

screen-shot-2017-03-02-at-1-09-15-pm

Oh another thing, make sure the Image is PNG, White color with a transparent back ground, so that you can edit the Tint as you go later if needed… 🙂

Title Text Font…

So for this one, I had to do a bit of playing around, which I found that “HelveticaNeue” and Font Size 17 is perfect for this. 🙂

Time for the coding… 😉

So let’s start off with loading the UIImage and initializing our UIButton.

// Load the Back arrow Image
var backBtnImage = UIImage.FromBundle("iosbackarrow.png");

backBtnImage = 
	backBtnImage.ImageWithRenderingMode(UIImageRenderingMode.AlwaysTemplate);

// Create our Button and set Edge Insets for Title and Image
var backBtn = new UIButton(UIButtonType.Custom)
{
	HorizontalAlignment = UIControlContentHorizontalAlignment.Left,
	TitleEdgeInsets = new UIEdgeInsets(11.5f, 15f, 10f, 0f),
	ImageEdgeInsets = new UIEdgeInsets(1f, 8f, 0f, 0f)
};

 

And set up the necessary Edge Insets for the button Title and Image as shown above. Well those values I figured out by playing around with the positioning values for hours.. 😛 lol

Next let’s dive into the Button’s customization…

// Set the styling for Title
// You could set any Text as you wish here
backBtn.SetTitle("Back", UIControlState.Normal);
// use the default blue color in ios back button text
backBtn.SetTitleColor(UIColor.FromRGB(0, 129, 249), UIControlState.Normal); 
backBtn.SetTitleColor(UIColor.LightGray, UIControlState.Highlighted);
backBtn.Font = UIFont.FromName("HelveticaNeue", (nfloat)17);

// Set the Image to the button
backBtn.SetImage(backBtnImage, UIControlState.Normal);

// Allow the button to Size itself
backBtn.SizeToFit();

 

Alright, that’s quite a bit of code to swallow, so first we set the Title Text of the button, and keep in mind you could set any Text as you wish there, for now I’m just using “Back” text.. 🙂

Next for the Text Color in the Normal state, I have used the default Blue color variation that iOS use by default, you could also use any color you prefer as well 🙂 Next we set the Highlight state of Text to Light Gray.

As we discussed at the beginning we will use HelveticaNeue with Font size of 17 for the Title Text. And finally set the Image to the Button and allow it to fit to the required size. 😀

// Add the Custom Click event you would like to 
// execute upon the Back button click
backBtn.TouchDown += (sender, e) =>
{
	// Whatever your custom back button click handling
};

 

Now here’s something very important, we need to make sure we handle our custom back button click as shown above… 😉

So next we shall do the preparation for the Frame.

//Set the frame of the button
backBtn.Frame = new CGRect(
	0,
	0,
	UIScreen.MainScreen.Bounds.Width / 4,
	NavigationController.NavigationBar.Frame.Height);

// Add our button to a container
var btnContainer = new UIView(
	new CGRect(0, 0, backBtn.Frame.Width, backBtn.Frame.Height));
btnContainer.AddSubview(backBtn);

 

So there we are adding the Frame values to our Button, where as I’m setting the width to a quarter of the Screen width, and as of the Height, I’m retrieving the NavigationBar’s height for it.

Next we need to add our UIButton to a UIView container as show above and make sure it has the same Height and Width as our UIButton.

Time to wrap things up fellas…

// A dummy button item to push our custom  back button to
// the edge of screen (sort of a hack)
var fixedSpace = new UIBarButtonItem(UIBarButtonSystemItem.FixedSpace)
{
	Width = -16f
};
// wrap our custom back button with a UIBarButtonItem
var backButtonItem = new UIBarButtonItem("", UIBarButtonItemStyle.Plain, null)
{
	CustomView = backBtn
};

// Add it to the ViewController
NavigationController.TopViewController.NavigationItem.LeftBarButtonItems 
= new[] { fixedSpace, backButtonItem };

 

So here’s the final steps, we are wrapping our button’s uiview container inside the UIBarButtonItem by setting it to the CustomView property. And then add it to the LeftBarButtonItems , which overrides the default existing Back Button.

Now you may wonder why there’s another UIBarButtonItem with the Width set to -16 value, this is actually to forcefully push our custom back button to the edge of the Navigation Bar. 😀 So that right, it is more of a hack to get the job done… 😉

See it in action…

So here’s our Custom iOS Back Button in action… 😀

screen-shot-2017-03-02-at-12-16-10-pm

Just for the sake of comparing here’s the default system Back Button in iOS…

screen-shot-2017-03-02-at-12-15-54-pm

Looks almost identical yeah! 😀

Well, that’s it fellas!

Enjoy! 😀

PS: I may have gotten some help from these posts on StackOverflow:

http://stackoverflow.com/questions/18384488/ios-7-uibarbutton-back-button-arrow-color
http://stackoverflow.com/questions/227078/creating-a-left-arrow-button-like-uinavigationbars-back-style-on-a-uitoolba

Le silly meaningless random string generator…

So here’s something I put together quickly by grabbing from stackoverflow, to generate some meaningless random string based on a given length of letters. 😀 This is actually a simple dot net implementation where as you could use it as a static class and use it anywhere you want. may be? up to you!

Here it is!

namespace WhateverYourNamespace
{
    public static class RandomWordGenerator
    {
        /// <summary>
        /// Just to generate some random words! 😛
        /// </summary>
        /// <param name="requestedLength"></param>
        /// <returns></returns>
        public static string GetMeaninglessRandomString(int requestedLength)
        {
            Random rnd = new Random();
            string[] consonants = { "b", "c", "d", "f", "g", "h", "j", "k",
                "l", "m", "n", "p", "q", "r", "s", "t", "v", "w", "x", "y", "z" };
            string[] vowels = { "a", "e", "i", "o", "u" };

            string word = "";

            if (requestedLength == 1)
            {
                word = GetRandomLetter(rnd, vowels);
            }
            else
            {
                for (int i = 0; i < requestedLength; i += 2)
                {
                    word += GetRandomLetter(rnd, consonants) + 
                        GetRandomLetter(rnd, vowels);
                }

                word = word.Replace("q", "qu").Substring(0, requestedLength);
                // We may generate a string longer than requested length, 
                // but it doesn't matter if cut off the excess.
            }

            return word;
        }

        private static string GetRandomLetter(Random rnd, string[] letters)
        {
            return letters[rnd.Next(0, letters.Length - 1)];
        }
    }
}

 

Now I don’t own this original implementation, I just put it into a static class and used in one of my apps. Sorry I don’t have the actual source of it. 😦 but I do recall I grab it from stackoverflow.

Anyways use it as you wish.

KTHANKSBYE!

lol

So I played around with Xamarin Forms Control Templates!

Yes I did and I came up with something pretty cool. Do you want to change your app’s theme on demand at run time? or load a different template for your pages at run time? or even simply change the app’s colors on demand?

Oh yeah Xamarin Forms Control Template gives the answer to all of that! 😉 Here what I built with it! 😀

xf-control-templates-ios xf-control-templates-android

Pretty cool eh! 😀

So basically what I built was a simple app where you could dynamically change the App background  color theme and change the change the App theme style on demand.

As you can see you can change the color theme of the app by clicking on the color buttons and change the theme style by clicking on the theme change button, which loads a different theme for the App if you closely notice.

The honest inspiration for this is that I remember back in the days when I was installing Windows 8 in my laptop, at the first time boot up, they ask you to choose the color theme you would like to use.

installation-7

Where it presents you with a beautiful color pallet and when you click on any of those colors the whole page changes the color accordingly, so I wanted to build something like that for the fun someday. 😉

So here we go… 😀

What are Xamarin Forms Control Templates?

Xamarin.Forms control templates provide the ability to easily theme and re-theme application pages at runtime. – Xamarin Docs 

Nuff said, if you want to learn more about it, read the documents. Here I’m going to explain how you could achieve the above cool stuff using Control Templates for Xamarin Forms.

Xamarin Forms Control Templates Binding?

I have used the Binding in order to change the template color at runtime. 🙂 If you’re not familiar with this concept, you may read up here: Xamarin Docs

We are keeping a public Property for the Theme color in our ContentPage, and binding our Control Template’s color values to that property. So at the run time whenever we change the Color property, it will get reflected to whatever the Template and the background color will change accordingly. 😉

Otherwise we would have to create different Control Templates for every single color, which will be very heavy and long code, but thanks to Binding we could do it with ease as described above.

Let me walk you through…

1. Creating templates…

First of all let’s create our templates, we are going to create two templates with different styles, as show in the below screenshots of the finished implementation.

simulator-screen-shot-1-jan-2017-2-53-32-pm  simulator-screen-shot-1-jan-2017-2-53-45-pm

  1. Template Header and footer will have a background and simple Label for both header and footer.
  2. Template Header will have one label with with a white background color, and footer will have two labels with white background color.

For now just forget about the color and we will focus on the initial Template Design.

Alright now let’s get to work.

Let’s begin by creating the project, and make sure to create XAML based Xamarin Forms project. Then let’s create our Control Templates in the App.xaml file, within the Application.Resources tag by adding them to the global ResourceDictionary, so that they could be accessed in anywhere of the app at runtime.

You can create any number of templates as you wish and name them in anyways you prefer. 😉 More themes the merrier…

<Application.Resources>
<ResourceDictionary>

  <!--template theme 1-->
  <ControlTemplate x:Key="MyTemplate1">
    ...
  </ControlTemplate>

  <!--template theme 2-->
  <ControlTemplate x:Key="MyTemplate2">
    ...
  </ControlTemplate>

</ResourceDictionary>
</Application.Resources>

 

le template 1…

Alright let’s create our first Control Template.

<!--template theme 1-->
<ControlTemplate x:Key="MyTemplate1">
<Grid>
  <Grid.RowDefinitions>
    <RowDefinition Height="0.1*" />
    <RowDefinition Height="0.8*" />
    <RowDefinition Height="0.1*" />
  </Grid.RowDefinitions>
  <Grid.ColumnDefinitions>
    <ColumnDefinition Width="0.05*" />
    <ColumnDefinition Width="0.95*" />
  </Grid.ColumnDefinitions>

  <!--template header-->
  <!--use of template binding for color-->
  <BoxView Grid.ColumnSpan="2" Color="{TemplateBinding Parent.ThemeColor}" />
  <Label Grid.Row="0" Grid.Column="1"
         Text="this is my theme style 1"
         TextColor="White"
         VerticalOptions="Center" />
  <!--template header-->

  <!--your page content goes in here-->
  <ContentPresenter Grid.Row="1" Grid.Column="0" Grid.ColumnSpan="2" />

  <!--template footer-->
  <!--use of template binding for color-->
  <BoxView Grid.Row="2" Grid.Column="0" Grid.ColumnSpan="2" Color="{TemplateBinding Parent.ThemeColor}" />
  <Label Grid.Row="2" Grid.Column="1"
         Text="template 1 (c) Udara Alwis 2016"
         TextColor="White"
         VerticalOptions="Center" />
  <!--template footer-->
</Grid>
</ControlTemplate>

 

There you have it, as you can see we have created a template with a Grid where we are aligning the page content in the middle  as the ContentPrensenter and the Header and Footer accordingly at top and bottom. We have added simple Labels to each Header and Footer with some text in it.

You can also notice that we are using Template property Binding to set the Background color of our Template. Color=”{TemplateBinding Parent.ThemeColor}”

So at the run time the Color will change according to the “ThemeColor” property which we will be implementing in the ContentPage.

You can use Binding to Change any property in your Control Templates thanks to awesomeness of Xamarin Forms! 😀

le template 2…

Now here’s our second Control Template.

<!--template theme 2-->
<ControlTemplate x:Key="MyTemplate2">
<Grid>
  <Grid.RowDefinitions>
	<RowDefinition Height="0.1*" />
	<RowDefinition Height="0.8*" />
	<RowDefinition Height="0.1*" />
  </Grid.RowDefinitions>
  <Grid.ColumnDefinitions>
	<ColumnDefinition Width="0.05*" />
	<ColumnDefinition Width="0.35*" />
	<ColumnDefinition Width="0.55*" />
	<ColumnDefinition Width="0.05*" />
  </Grid.ColumnDefinitions>

  <!--template header-->
  <!--use of template binding for color-->
  <BoxView Grid.ColumnSpan="4" Color="{TemplateBinding Parent.ThemeColor}" />
  <Label Grid.Row="0" Grid.Column="1"  Grid.ColumnSpan="2"
		 Text="this is my theme style 2"
		 TextColor="Black"
		 BackgroundColor="White"
		 VerticalOptions="Center" />
  <!--template header-->

  <!--your page content goes in here-->
  <ContentPresenter Grid.Row="1" Grid.Column="0" Grid.ColumnSpan="4" />

  <!--template footer-->
  <!--use of template binding for color-->
  <BoxView Grid.Row="2" Grid.Column="0" Grid.ColumnSpan="4" Color="{TemplateBinding Parent.ThemeColor}" />
  <Label Grid.Row="2" Grid.Column="1"
		 Text="template 2"
		 TextColor="Black"
		 BackgroundColor="White"
		 VerticalOptions="Center" />
  <Label Grid.Row="2" Grid.Column="2"
		 Text="(c) Udara Alwis 2016"
		 TextColor="Black"
		 BackgroundColor="White"
		 VerticalOptions="Center"/>
  <!--template footer-->
</Grid>
</ControlTemplate>

 

As you can see the difference of this Template is that we have added extra columns to the Grid container and added extra labels to fill in. Also you may have noticed that we are setting the Label background to White color in this template.

Alright there goes our two templates in this example. Next let’s implement the design for our ContentPage.

2. ContentPage design stuff…

So those two Template themes are now ready to be applied for any ContentPage in our App.

Next let’s lay down the design for our content page. Remember hence we are using Control Templates, we need to implement our UI in a way our page could use those templates, which is by,

having a ContentView which will position itself in the ContentPresenter in the Templates once we bind to them.

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:local="clr-namespace:XFControlTemplateThemes"
             x:Class="WhateverYourNamespace.MainPage">

  <ContentView x:Name="contentView"
               ControlTemplate="{StaticResource MyTemplate1}">
    <ContentView.Padding>
      <OnPlatform x:TypeArguments="Thickness" iOS="0,20,0,0" />
    </ContentView.Padding>

   <!-- Your Page Content-->

  </ContentView>
</ContentPage>

 

You may have noticed that I have bound our ContentView ControlTemplate  property to one of the Templates we created in the App.xaml yeah? Yep exactly that’s because since we placed those templates in the App’s global level, we can directly access those properties from anywhere in our app. So as of the defualt ControlTemplate I have set it to the “MyTemplate1” template we created. So when the page loads it will be decorated with that. 😉

Now let’s take a look at the Page content design which will be placed inside the ContentView above. 🙂

Now keep in mind you can implement whatever the design you want to your Page body, but for this example basically we need to have a button to switch in between the two themes we created above and another bunch of buttons to change the color of those themes (something like a color pallet). So here we go…

<StackLayout VerticalOptions="CenterAndExpand" Padding="10,0,10,0">

  <Label Text="Welcome to the Dynamic Theme Changer app!"
		 HorizontalTextAlignment="Center"
		 FontSize="20"
		 VerticalOptions="Start"
		 HorizontalOptions="Center" />

  <Grid Padding="0,20,0,20">
	<Label Text="click below to change the theme on the go"
		   HorizontalTextAlignment="Center"
		   HorizontalOptions="Center" />
	<Button Text="change current theme template" Grid.Row="1"
				Clicked="OnButtonClicked" />

	<Grid.RowDefinitions>
	  <RowDefinition Height="*" ></RowDefinition>
	  <RowDefinition Height="40" ></RowDefinition>
	</Grid.RowDefinitions>
  </Grid>

  <Grid Padding="0,20,0,20">

	<Label Text="click below to change the theme color on the go"
		   HorizontalTextAlignment="Center"
		   HorizontalOptions="Center"
		   Grid.Row="0" Grid.Column="0" Grid.ColumnSpan="10"/>

	<Button BackgroundColor="#ff0000" Grid.Row="1" Grid.Column="0" Clicked="OnColorChangeButtonClicked" />
	<Button BackgroundColor="#ff8000" Grid.Row="1" Grid.Column="1" Clicked="OnColorChangeButtonClicked" />
	<Button BackgroundColor="#ffff00" Grid.Row="1" Grid.Column="2" Clicked="OnColorChangeButtonClicked" />
	<Button BackgroundColor="#00ff40" Grid.Row="1" Grid.Column="3" Clicked="OnColorChangeButtonClicked" />
	<Button BackgroundColor="#00ffff" Grid.Row="1" Grid.Column="4" Clicked="OnColorChangeButtonClicked" />
	<Button BackgroundColor="#0080ff" Grid.Row="1" Grid.Column="5" Clicked="OnColorChangeButtonClicked" />
	<Button BackgroundColor="#4000ff" Grid.Row="1" Grid.Column="6" Clicked="OnColorChangeButtonClicked" />
	<Button BackgroundColor="#bf00ff" Grid.Row="1" Grid.Column="7" Clicked="OnColorChangeButtonClicked" />
	<Button BackgroundColor="#ff0080" Grid.Row="1" Grid.Column="8" Clicked="OnColorChangeButtonClicked" />
	<Button BackgroundColor="#ff0040" Grid.Row="1" Grid.Column="9" Clicked="OnColorChangeButtonClicked" />

	<Grid.RowDefinitions>
	  <RowDefinition Height="*" />
	  <RowDefinition Height="40" />
	</Grid.RowDefinitions>
	<Grid.ColumnDefinitions>
	  <ColumnDefinition Width="0.1*" />
	  <ColumnDefinition Width="0.1*" />
	  <ColumnDefinition Width="0.1*" />
	  <ColumnDefinition Width="0.1*" />
	  <ColumnDefinition Width="0.1*" />
	  <ColumnDefinition Width="0.1*" />
	  <ColumnDefinition Width="0.1*" />
	  <ColumnDefinition Width="0.1*" />
	  <ColumnDefinition Width="0.1*" />
	  <ColumnDefinition Width="0.1*" />
	</Grid.ColumnDefinitions>
  </Grid>

</StackLayout>

 

Behold my beautiful UI. 😉 As you can see the first button will be switching in between the themes we created before, and them there’s a whole another set of buttons (color pallet buttons) with different background colors, which points to the same click event. Those buttons will be changing the template color by changing the ThemeColor property I mentioned earlier, which we are going to implement next. 🙂

3. ContentPage code-behind…

Now this is where we put things together, in your MainPage.cs code behind. Which we are handling all the theme changes and color changes on the go. 😉

So here are what we are going to implement here…

  1. ThemeColor public property to be used by the Templates for Color changing feature
  2. Load the control templates to be used in this page for run time theme changing
  3. Handle the run time theme switching functionality (switch the themes in between the templates we created before)
  4. Handle the tun time them color switching functionality (switch the themes between different color as show in those color buttons)
public partial class MainPage : ContentPage
{
	public static readonly BindableProperty ThemeColorProperty =
		BindableProperty.Create("ThemeColor", typeof(Color), typeof(MainPage), Color.Red);
	/// <summary>
	/// Gets or Sets the theme color for the template
	/// </summary>
	public Color ThemeColor
	{
		set { SetValue(ThemeColorProperty, value); }
		get { return (Color)GetValue(ThemeColorProperty); }
	}

	private bool _originalTemplate = true;
	private ControlTemplate _myTemplate1;
	private ControlTemplate _myTemplate2;

	public MainPage()
	{
		InitializeComponent();

		_myTemplate1 = (ControlTemplate)Application.Current.Resources["MyTemplate1"];
		_myTemplate2 = (ControlTemplate)Application.Current.Resources["MyTemplate2"];
	}

	void OnButtonClicked(object sender, EventArgs e)
	{
		// switching to the next theme
		_originalTemplate = !_originalTemplate;
		contentView.ControlTemplate = (_originalTemplate) ? _myTemplate1 : _myTemplate2;
	}

	private void OnColorChangeButtonClicked(object sender, EventArgs e)
	{
		if (((Button)sender) != null)
		{
			var sender1 = ((Button)sender);

			// Change the theme color according 
			// to the selected button color
			ThemeColor = sender1.BackgroundColor;

			// this will update the ThemeColor property
			// and reflect to the Control template
		}
	}
}

 

You can see I have implemented the ThemeColor property where our Templates will be binding their Color properties to. Then take a look at the event OnColorChangeButtonClicked which is the event that is fired by the set of buttons with different colors as we implemented in the UI. So inside this event we are retrieving the button’s background color and setting that value to our ThemeColor property, which will in return reflect to the Template that has been loaded to the page at that moment.

And then in the Constructor we are loading the two templates we created before into our page by accessing the Application Resources dictionary so we can use those instances to change the them on the go.

Inside the OnButtonClicked event we are switching between the two template themes we have loaded above.

Finally hit F5!

Alright that’s it for the coding. Now save it and hit F5 to see the magical beauty of Xamarin Forms! 😉

xf-control-templates-ios  xf-control-templates-android

So you can see clearly that when you click on the “change current theme template” button, the theme immediately changes to the next template.

And then you click on any of the color pallet buttons you can see the theme background color changes accordingly. Beautiful isn’t it? 😉

There you have it fellas!

Now as for them lazy people, you could straight away grab the code up in my github: Xamarin-Playground/XFControlTemplateThemes

Enjoy and share! 😀

– Udara Alwis

Listening to the Layout on Xamarin Android PageRenderer! (LayoutListener)

So when you create a Custom Renderer for your Xamarin Forms ContentPage, on Android, sometimes you have to tap into the Android Layout changes on your current page.

For instances like, Orientation changes, Keyboard visibility changes on Android and so on.

This is done by Adding a Layout Listener to our Layout’s ViewTree. 🙂 Confusing? Let’s get to work!

Create a Layout Listener…

First let’s create our Layout Listener, the guy who get’s the call back when the Layout Changes on the ViewTree of our Layout.

public class CustomLayoutListener : Java.Lang.Object, ViewTreeObserver.IOnGlobalLayoutListener
{
	public void OnGlobalLayout()
	{
		// do whatever the stuff you wanna do here
	}
}

 

We derive to from the IOnGlobalLayoutListener interface, where as you need to implement its OnGlobalLayout() method which get’s the call back when a Layout change occurs.

Add the Listener to the ViewTree…

Next add it to the ViewTreeObserver of your Layout.

[assembly: ExportRenderer(typeof(CustomContentPage), typeof(CustomContentPageRenderer))]
namespace WhateverYourNamespace
{
    public class CustomContentPageRenderer : PageRenderer
    {
        protected override async void OnElementChanged(ElementChangedEventArgs<Page> e)
        {
			var rootView = CrossCurrentActivity.Current.Activity.Window.DecorView.RootView;
			rootView.ViewTreeObserver.AddOnGlobalLayoutListener(new CustomLayoutListener());
		}
	}
}

 

Since I implemented this on a Xamarin Forms Custom Renderer, first I have gained access to the current Activity’s RootView (from a 3rd party library CurrentActivityPlugin) and then I have added my listener to the ViewTreeObserver of my root view. 😀

TADAA! 😀

but you could also…

Oh well good things comes to those who wait.. lol Xamarin Android provides you an event called GlobalLayout where you could also directly subscribe to Layout changes without having to implement your own listener.

rootView.ViewTreeObserver.GlobalLayout += (sender, args) =>
{
	// do whatever the stuff you wanna do here
}

 

Oh well it depends on your implementation requirement though.

Anyways there you have it! 😀

Enjoy!

Setting RelativeLayout ConstraintExpressions from XAML Styles in Xamarin Forms…

When it comes to Xamarin Forms RelativeLayout we always use Constraints, its pretty easy to add those Constraint values from C# code behind, but when it comes to XAML UI implementation, it’s not so easy.

so myself…

I have been working with XAML UI implementation for the last year or so, specially dealing with a lot of pixel perfect design, which needs a lot of customization to design from XAML. But as a developer you have to find ways to deal with those stuff. In my current project we practice a strict discipline of MVVM pattern, which we strongly separate XAML UI View and the ViewModel code. So under no exceptions we add any single C# UI code or XAML code behind implementations in our project.

complex design implementations…

When you have to deal with complex design implementations in Xamarin Forms, the best way to go is with RelativeLayout, along with Relative Constraint values for X/Y position and Height/Width values.

flag1

RelativeLayout is good…

Usually those RelativeLayout Constraint values manages to get the job done, with ease on both Android and iOS devices. But sometimes it doesn’t quite go right, specially with Android, where you have to deal with different types of screen resolutions.

layouts1

but sometimes…

So at times like that you need to specify RelativeLayout ConstraintExpression separately for iOS and Android devices. But how do you do this in XAML code?

so how?

So how do you set those ConstraintExpression right from XAML code? Styles is the answer! 😀

The trick is to create two different Styles for Android and iOS, targeting the control you need to set the RelativeLayout Constraints on.

And then on your control’s XAML declaration, you set the Style property using the OnPlatform tag accordingly for iOS and Android.

Let’s do it…

You could define these Styles on your Page level or Application level as you wish as shown below…

You can see I have created twp styles which targets the Label control type and added my Relative Layout ConstraintExpressions. 🙂 Also I have added the other Properties that I need to customize through these Styles.

<ContentPage.Resources>
	<ResourceDictionary>
		<Style x:Key="MyLabelStyleiOS" TargetType="Label">
		  <Setter Property="BackgroundColor" Value="Yellow"/>
		  <Setter Property="HorizontalTextAlignment" Value="Center"/>
		  <Setter Property="RelativeLayout.YConstraint" 
				  Value="{ConstraintExpression RelativeToParent,Property=Height,Factor=0.5}"/>
		  <Setter Property="RelativeLayout.WidthConstraint"
				  Value="{ConstraintExpression RelativeToParent,Property=Width,Factor=0.7}"/>
		  <Setter Property="RelativeLayout.XConstraint"
				  Value="{ConstraintExpression RelativeToParent,Property=Width,Factor=0.15}"/>
		</Style>

		<Style x:Key="MyLabelStyleAndroid" TargetType="Label">     
		  <Setter Property="BackgroundColor" Value="Yellow"/>
		  <Setter Property="HorizontalTextAlignment" Value="Center"/>
		  <Setter Property="RelativeLayout.YConstraint"
				  Value="{ConstraintExpression RelativeToParent,Property=Height,Factor=0.1}"/>
		  <Setter Property="RelativeLayout.WidthConstraint"
				  Value="{ConstraintExpression RelativeToParent,Property=Width,Factor=0.7}"/>
		  <Setter Property="RelativeLayout.XConstraint"
				  Value="{ConstraintExpression RelativeToParent,Property=Width,Factor=0.15}"/>
		</Style>
	</ResourceDictionary>
</ContentPage.Resources>

 

And then on the your Control that you need to set those RelativeLayout Constraints…

<Label Text="Welcome to the app!"  >
	<Label.Style>
	  <OnPlatform x:TypeArguments="Style"
				  iOS="{StaticResource MyLabelStyleiOS}"
				  Android="{StaticResource MyLabelStyleAndroid}" />
	</Label.Style>
</Label>

 

You can see how I have nested down the Style property and added the specific style according to the Platform type.

It’s very important to notice that I have added those Styles as StaticResource this is because we need to set those RelativeLayout ConstraintExpressions before the run time, while the XAML are being parsed. 🙂 Once the XAML layout is parsed, we can not set the ConstraintExpressions, since it’s not going to be rendered.

make it pretty… Generalize!

Yep the above styles are ugly, so let’s generalize it and move the common properties and constraints to a general style as below, and derive our child styles.

<Style x:Key="MyLabelStyle" TargetType="Label">
  <Setter Property="BackgroundColor" Value="Yellow"/>
  <Setter Property="HorizontalTextAlignment" Value="Center"/>
  <Setter Property="RelativeLayout.WidthConstraint"
		  Value="{ConstraintExpression RelativeToParent,Property=Width,Factor=0.7}"/>
  <Setter Property="RelativeLayout.XConstraint"
		  Value="{ConstraintExpression RelativeToParent,Property=Width,Factor=0.15}"/>
</Style>

<Style x:Key="MyLabelStyleiOS" TargetType="Label" BasedOn="{StaticResource MyLabelStyle}">
  <Setter Property="RelativeLayout.YConstraint" 
		  Value="{ConstraintExpression RelativeToParent,Property=Height,Factor=0.5}"/>
</Style>

<Style x:Key="MyLabelStyleAndroid" TargetType="Label" BasedOn="{StaticResource MyLabelStyle}">
  <Setter Property="RelativeLayout.YConstraint"
		  Value="{ConstraintExpression RelativeToParent,Property=Height,Factor=0.1}"/>
</Style>

 

There we go! now that’s beautiful. Always keep in mind to generalize the common Style properties, and here in this case the common ConstraintExpression values. 🙂

Cheers! 😀

How to add a fixed Background Image for a UIScrollView?

So recently I wanted to add a Fixed image behind a ScrollView in Xamarin Forms. Furthermore when the ScrollView is scrolling the background image shouldn’t scroll along with it, and background image should stay fixed while the content is scrolling.

Solution?

So the obvious solution would be to lay down a RelativeLayout and top of that Image, and then a ScrollView with Transparent background.

But I wanted…

but instead of laying out all those layouts and multiple controls, I wanted to achieve this right from one Control, by customizing the ScrollView accordingly.

So I got to into Coding…

So I created a Custom ScrollView control in PCL project and added the Custom Renderers for each platform iOS and Android. Although I got it working with ease in on Android by setting the Image as the Background drawable for the ScrollView, I was having some struggle with iOS.

trouble with iOS UIScrollView…

So the Xamarin Forms ScrollView’s native iOS mapped control is the UIScrollView. So I tried adding the a UIImageView to the UIScrollView from the custom renderer hoping it should get the job done according to theory.

but the background was panning across the Content size. And it started scrolling alone with the Content.

So let me walk you through what I tried and what actually worked… 🙂

1. Adding the UIImageView as a SubView

So as per the obvious solution I added the UIImage into a UIImageView and added it into the UIScrollView as a SubView as shown below. Also you may have noticed how I have called SendSubviewToBack method to place the UIImageView behind the UIScrollView.

protected override async void OnElementChanged(VisualElementChangedEventArgs e)
{
	base.OnElementChanged(e);

	if (e.NewElement != null)
	{
		var _uiImageViewBackground = new UIImageView(_uiImageBackground);

		this.AddSubview(_uiImageViewBackground);
		this.SendSubviewToBack(_uiImageViewBackground);
	}
}

 

And this was the result as you can see below..

method1

As you can see the UIImageView takes up the Height of the UIScrollView Content, not the UIScrollView actual Height, thereby resulting of the UIImageView spanning across the whole Content size. :O

2. Resizing the UIImage and adding the UIImageView as a SubView

Then I thought what if I resized the Image to the actual Height and Width of the UIScrollView and added as a Subview as show below.

Now in an iOS Custom Renderer we can not access the UIScrollView’s Bounds or Frame right from the OnElementChanged method, we need to override the Draw() method, which provides the Height and Width since it’s actually being drawn on the Parent view.

public override void Draw(CGRect rect)
{
	base.Draw(rect);

	// resize the UIImage to fit the current UIScrollView's width and height
	_uiImageBackground = ResizeUIImage(_uiImageBackground, (float)rect.Width, (float)rect.Height);

	var _uiImageViewBackground = new UIImageView(_uiImageBackground);

	this.AddSubview(_uiImageViewBackground);
	this.SendSubviewToBack(_uiImageViewBackground);
}

 

So as you can see I have resized the UIImage and added it to the UIScrollView thought a UIImageView holder.

Look at the results…

method2

Well the Background Image has been resized but the Background View still scrolls with the Content of UIScrollView. 😦

3. How about InsertSubview() ?

There are couple of methods for Adding a SubView to a View, the most common used one is the AddSubView() method which is also an alias for Add().

Then there also another method call we could use, InsertSubview(). In theory it does the same thing as AddSubView() but in a different manner where you could define a View index, in terms of which index the View should be added to in the array of sub-views in the given View.

So instead of this,

this.AddSubview(_uiImageViewBackground);
this.SendSubviewToBack(_uiImageViewBackground);

 

Let’s call the below, as you can see I’m placing our UIImageView at the very bottom of the SubViews stack by giving index 0 value.

this.InsertSubview(_uiImageViewBackground, 0);

 

Oh well what did you expect! Same result as before. 😦

4. How about InsertSubviewBelow() ?

So this method is also somewhat similar to above, where as this allows you to straightaway as a Subview, and define underneath which SubView you need to add your View in the stack. 😀

So I tried this as well. By the “this” reference I’m referring to the UIScrollView as the sibling and to tell the layout engine to place the UIImageView below the UIScrollView. 🙂

this.InsertSubviewBelow(_uiImageViewBackground, this);

 

But unfortunately the results was the same… 😦

5. What about directly setting the Background?

Frustrated with trying to add SubViews approach, I thought of directly setting the Background property of UIScrollView, specifically set the UIImage directly to the BackgroundColor Property of UIScrollView.

Well there’s no way we could set the BackgroundColor property from the Draw() method override, hence the canvas is already drawn. So we need to set it before its being drawn.

So let’s move back to the OnElementChanged method and set the BackgroundColor.

Since there’s no availability of the Height and Width values within the OnElementChanged event firing, for now we’ll just directly set the UIImage to BackgroundColor without resizing.

protected override async void OnElementChanged(VisualElementChangedEventArgs e)
{
	base.OnElementChanged(e);

	if (e.NewElement != null)
	{
			this.BackgroundColor = UIColor.FromPatternImage(_uiImageImageBackground);
	}
}

 

Oh well, look at the results. It also fills up the whole Content area, without just setting the “background” on UIScrollView.

method3

5. What about directly setting the Background with resized UIImage?

Alright now let’s get a bit serious and retry the above approach properly, by accessing the Height and Width of the UIScrollView and resizing the UIImage accordingly.

So to do this we need to tap into the place where the Height and Width first gets allocated before the Draw method. That’s by subscribing to the OnPropertyChanged() as shown below.

protected override async void OnElementChanged(VisualElementChangedEventArgs e)
{
	base.OnElementChanged(e);

	if (e.NewElement != null)
	{
		((CustomScrollView)e.NewElement).PropertyChanged += OnPropertyChanged;
	}
}

private void OnPropertyChanged(object sender, PropertyChangedEventArgs propertyChangedEventArgs)
{
	if (propertyChangedEventArgs.PropertyName == CustomScrollView.HeightProperty.PropertyName)
	{
		// check if the Width and Height are assigned
		if (((CustomScrollView)sender).Width > 0 & ((CustomScrollView)sender).Height > 0)
		{
			// resize the UIImage to fit the current UIScrollView's width and height
			_uiImageImageBackground = ResizeUIImage(_uiImageImageBackground, (float)((CustomScrollView)sender).Width, (float)((CustomScrollView)sender).Height);

			// Set the background Image
			this.BackgroundColor = UIColor.FromPatternImage(_uiImageImageBackground);
		}
	}
}

 

So inside the OnPropertyChanged() event we are waiting till the Width and Height properties are available, as you can see we are looking for the PropertyName in the event args. Then we resize the UIImage according to the retrieved Height and Width and values of UIScrollView and set the UIImage to the Background.

method4

Now as you can see, the Background Image gets resized to the exact size of UIScrollView but the Background is still scrolling with the content. And if you notice closely, you can see the Background has repeated the Image, this is because of the UIColor.FromPatternImage() where as the UIImage gets repeated to fill the whole canvas. This means that the Background still gets spread across the whole Content area of the UIScrollView.

then I witnessed something strange….

What actually worked… (strangely though)

So meanwhile playing around with different override methods and properties, at some point….

I accidentally left the Draw() method overridden in my Custom Renderer as shown below, and moved the setting of the UIScrollView Background to the OnPropertyChanged event like I did in the previous step.

protected override async void OnElementChanged(VisualElementChangedEventArgs e)
{
	base.OnElementChanged(e);

	if (e.NewElement != null)
	{
		((CustomScrollView)e.NewElement).PropertyChanged += OnPropertyChanged;
	}
}

private void OnPropertyChanged(object sender, PropertyChangedEventArgs propertyChangedEventArgs)
{
	if (propertyChangedEventArgs.PropertyName == CustomScrollView.HeightProperty.PropertyName)
	{
		// check if the Width and Height are assigned
		if (((CustomScrollView)sender).Width > 0 & ((CustomScrollView)sender).Height > 0)
		{
			// resize the UIImage to fit the current UIScrollView's width and height
			_uiImageImageBackground = ResizeUIImage(_uiImageImageBackground, (float)((CustomScrollView)sender).Width, (float)((CustomScrollView)sender).Height);

			// Set the background Image
			this.BackgroundColor = UIColor.FromPatternImage(_uiImageImageBackground);
		}
	}
}

//We need to override this to have the background image to be fixed
public override void Draw(CGRect rect)
{
	base.Draw(rect);
}

 

As you can see in my above code, I have just overriden the Draw() event and left it just as it is, without writing any code inside the method.

And behold! 😀 IT WORKED! 😀

bloopscrollview-on-ios-lowq

TADAA! 😀 as you can see we have successfully got it to work, a fixed background image in UIScrollView. 😉

Although this does not make any sense, how could the Background of the UIScrollView prevents itself from scaling to the size of Content size just by simply overriding the Draw() event, without even executing any code inside of it.

Either way this trick got the work done. 😀 May be this is just a bug in Xamarin or iOS. 😛

There you have it, how to add a fixed background image to a UIScrollView from custom renderer in Xamarin! 🙂

Enjoy!

An improved ScrollView control for Xamarin Forms by me, myself and I…

Alright now when it comes to the default Xamarin Forms ScrollView, its pretty much generic and limited with the simple common attributes and behaviours, and it does not deliver any specific “cool” features with it.

What’s so cool about it?

So I thought of creating my own Custom ScrollView for Xamarin Forms using Custom Renderers, which would include the following awesome features,

Bouncy Effect – Yeah you gotta admit, the bounce effect of a native scrollview is pretty fun to play with, in a User’s perspective. So I thought of enabling this feature in my custom ScrollView even when the Child Element doesn’t exceeds the ScrollView boundaries… 😉
(PS: this effect is interpreted in native Android and iOS differently)

Disabling and Enabling Horizontal and Vertical Scroll Indicators – Now sometimes these scroll bar indicators are useful but there are times which we want to hide them, as it might look ugly on the UI in certain cases. So yeah let’s have some control over it shall we? 😀

Background Image – Of course who wouldn’t like a background Image on a Scroll view eh! 😉 Well to be specific we are going to add a Fixed Background Image for the ScrollView. And note that this background Image would be fixed, and will not be scrolling with the Content of the ScrollView. (I will do another post to enable that feature).

Yes behold, me, myself and I presenting the “BloopyScrollView” why the name “BloopyScrollView”? I don’t even know. lol 😛

Implementation

Alright let’s go ahead and create our Custom ScrollView Control in the PCL project. Along with the following properties, so that we could have direct control over the above said behaviours.

Alright now expect this to be longer, since I have added the properties as Bindable Properties, so you could use them in any MVVM scenario with ease. 😀

namespace WhateverYourNamespace
{
    public class BloopyScrollView : ScrollView
    {
        public static readonly BindableProperty IsHorizontalScrollbarEnabledProperty =
        BindableProperty.Create(
            nameof(IsHorizontalScrollbarEnabled),
            typeof(bool),
            typeof(BloopyScrollView),
            false,
            BindingMode.Default,
            null);
        /// <summary>
        /// Gets or sets the Horizontal scrollbar visibility
        /// </summary>
        public bool IsHorizontalScrollbarEnabled
        {
            get { return (bool)GetValue(IsHorizontalScrollbarEnabledProperty); }
            set { SetValue(IsHorizontalScrollbarEnabledProperty, value); }
        }


        public static readonly BindableProperty IsVerticalScrollbarEnabledProperty =
        BindableProperty.Create(
            nameof(IsVerticalScrollbarEnabled),
            typeof(bool),
            typeof(BloopyScrollView),
            false,
            BindingMode.Default,
            null);
        /// <summary>
        /// Gets or sets the Vertical scrollbar visibility
        /// </summary>
        public bool IsVerticalScrollbarEnabled
        {
            get { return (bool)GetValue(IsVerticalScrollbarEnabledProperty); }
            set { SetValue(IsVerticalScrollbarEnabledProperty, value); }
        }


        public static readonly BindableProperty IsNativeBouncyEffectEnabledProperty =
        BindableProperty.Create(
            nameof(IsNativeBouncyEffectEnabled),
            typeof(bool),
            typeof(BloopyScrollView),
            true,
            BindingMode.Default,
            null);
        /// <summary>
        /// Gets or sets the Native Bouncy effect status
        /// </summary>
        public bool IsNativeBouncyEffectEnabled
        {
            get { return (bool)GetValue(IsNativeBouncyEffectEnabledProperty); }
            set { SetValue(IsNativeBouncyEffectEnabledProperty, value); }
        }


        public static readonly BindableProperty BackgroundImageProperty =
        BindableProperty.Create(
            nameof(BackgroundImage),
            typeof(ImageSource),
            typeof(BloopyScrollView),
            null,
            BindingMode.Default,
            null);
        /// <summary>
        /// Gets or sets the Background Image of the ScrollView
        /// </summary>
        public ImageSource BackgroundImage
        {
            get { return (ImageSource)GetValue(BackgroundImageProperty); }
            set { SetValue(BackgroundImageProperty, value); }
        }
    }
}

 

There we go IsHorizontalScrollbarEnabled, IsVerticalScrollbarEnabled to disable/enable Horizonal and Vertical Scrollbars.

IsNativeBouncyEffectEnabled to control the Native Bouncy effect.

BackgroundImage to set the ImageSource for the ScrollView’s background Image. And make sure to provide a proper image for this hence we will be resizing the given image in our native renderer level to fit to the background of the ScrollView.(You will see in the next steps below)

Alright let’s head over to creating the Custom Renderers associated with our BloopyScrollView.

Something to keep in mind…

So if you’re a frequent reader of my blog, you may remember sometime ago I created an Extention class for handling Xamarin Forms Images in Native code level: https://theconfuzedsourcecode.wordpress.com/2016/12/12/an-awesome-image-helper-to-convert-xamarin-forms-imagesource-to-ios-uiimage-or-android-bitmap/

Why I’m bringing this up, is because we are going to be needing it for this project. You ask why? Because we need to convert the above BackgroundImage, which is of type Xamarin Forms ImageSource.

So we need to convert that ImageSource to native UIImage or Bitmap image respectively in our Custom renderer levels. 😉

So go ahead and grab that code real quick and add it to your Native Projects. 😀

iOS Implementation

Now let’s create the Custom Renderer for the Control in Xamarin.iOS project.

[assembly: ExportRenderer(typeof(BloopyScrollView), typeof(BloopyScrollViewRenderer))]
namespace WhateverYourNamespace.iOS
{
    public class BloopyScrollViewRenderer : ScrollViewRenderer
    {
        private UIImage _uiImageImageBackground;

        protected override async void OnElementChanged(VisualElementChangedEventArgs e)
        {
            base.OnElementChanged(e);

            this.ShowsVerticalScrollIndicator = ((BloopyScrollView)e.NewElement).IsVerticalScrollbarEnabled;
            this.ShowsHorizontalScrollIndicator = ((BloopyScrollView)e.NewElement).IsHorizontalScrollbarEnabled;

            if (e.NewElement != null)
            {
                if (((BloopyScrollView)e.NewElement).IsNativeBouncyEffectEnabled)
                {
                    this.Bounces = true;
                    this.AlwaysBounceVertical = true;
                }

                if (((BloopyScrollView)e.NewElement).BackgroundImage != null)
                {
                    // retrieving the UIImage Image from the ImageSource by converting
                    _uiImageImageBackground = await IosImageHelper.GetUIImageFromImageSourceAsync(((BloopyScrollView)e.NewElement).BackgroundImage);
                }

                ((BloopyScrollView)e.NewElement).PropertyChanged += OnPropertyChanged;
            }
        }

        private void OnPropertyChanged(object sender, PropertyChangedEventArgs propertyChangedEventArgs)
        {
            if (propertyChangedEventArgs.PropertyName == BloopyScrollView.HeightProperty.PropertyName)
            {
                // check if the Width and Height are assigned
                if (((BloopyScrollView)sender).Width > 0 & ((BloopyScrollView)sender).Height > 0)
                {
                    // resize the UIImage to fit the current UIScrollView's width and height
                    _uiImageImageBackground = ResizeUIImage(_uiImageImageBackground, (float)((BloopyScrollView)sender).Width, (float)((BloopyScrollView)sender).Height);

                    // Set the background Image
                    this.BackgroundColor = UIColor.FromPatternImage(_uiImageImageBackground);
                }
            }
        }

        // We need to override this to have the background image to be fixed
        public override void Draw(CGRect rect)
        {
            base.Draw(rect);
        }

        // Resize the UIImage
        public UIImage ResizeUIImage(UIImage sourceImage, float widthToScale, float heightToScale)
        {
            var sourceSize = sourceImage.Size;
            var maxResizeFactor = Math.Max(widthToScale / sourceSize.Width, heightToScale / sourceSize.Height);
            if (maxResizeFactor > 1) return sourceImage;
            var width = maxResizeFactor * sourceSize.Width;
            var height = maxResizeFactor * sourceSize.Height;
            UIGraphics.BeginImageContext(new CGSize(width, height));
            sourceImage.Draw(new CGRect(0, 0, width, height));
            var resultImage = UIGraphics.GetImageFromCurrentImageContext();
            UIGraphics.EndImageContext();
            return resultImage;
        }
    }
}

 

Inside the method we are assigning the relevant properties of our BloopyScrollView to the native control properties.

The UIScrollView which is associated with the Xamarin Forms ScrollView has the following native properties:

  • ShowsVerticalScrollIndicator: Make the vertical scrollbar visible or hidden
  • ShowsHorizontalScrollIndicator: Make the horizontal scrollbar visible or hidden
  • Bounces: Always enable the native bounce effect on iOS UIScrollView
  • BackgroundColor: Allows to set the background color for the UIScrollView or set an Image as a pattern

Also you may have noted that we are converting our Image Source BackgroundImage to a UIImage using our extension.

And then when the Height and Width are set to the Control, we are resizing the Image to fit those properties and setting that as the Background of the UIScrollView through the UIColor.FromPatternImage() which allows us to set the image as a pattern throughout the canvas of the UIScrollView.

the strange tale of getting the UIScrollView’s Fixed background in Xamarin… :O

Notice that we are overriding the Draw(CGRect rect) method, this is to have the UIScroll Background Image to be fixed within the boundaries, and not to be spanned across the Content area.

Because usually if we set the BackgroundColor property, it will span across the Content area, but strangely if we override the Draw() method, BackgroundColor would only be contained within UIScrollView’s boundaries, without spanning across the Content area. This is something I figured out while playing around with the above implementation. 😀

Alright let’s jump into Android… 😀

Android Implementation

Now let’s create the Custom Renderer for the Control in Xamarin.Android project.

[assembly: ExportRenderer(typeof(BloopyScrollView), typeof(BloopyScrollViewRenderer))]
namespace WhateverYourNamespace.Droid
{
    public class BloopyScrollViewRenderer : ScrollViewRenderer
    {
        private Bitmap _bitmapImageBackground;

        protected override async void OnElementChanged(VisualElementChangedEventArgs e)
        {
            base.OnElementChanged(e);

            this.VerticalScrollBarEnabled = ((BloopyScrollView)e.NewElement).IsVerticalScrollbarEnabled;
            this.HorizontalScrollBarEnabled = ((BloopyScrollView)e.NewElement).IsHorizontalScrollbarEnabled;

            if (((BloopyScrollView)e.NewElement).IsNativeBouncyEffectEnabled)
            {
                this.OverScrollMode = OverScrollMode.Always;
            }

            if (((BloopyScrollView) e.NewElement).BackgroundImage != null)
            {
                // retrieving the Bitmap Image from the ImageSource by converting
                _bitmapImageBackground = await AndroidImageHelper.GetBitmapFromImageSourceAsync(((BloopyScrollView)e.NewElement).BackgroundImage, this.Context);

                // resize the Bitmap to fit the current ScrollView's width and height
                var _resizedBitmapImageBackground = new BitmapDrawable(ResizeBitmap(_bitmapImageBackground, this.Width, this.Height));

                // Set the background Image
                this.Background = _resizedBitmapImageBackground;
            }
        }

        // Resize the Bitmap
        private Bitmap ResizeBitmap(Bitmap originalImage, int widthToScae, int heightToScale)
        {
            Bitmap resizedBitmap = Bitmap.CreateBitmap(widthToScae, heightToScale, Bitmap.Config.Argb8888);

            float originalWidth = originalImage.Width;
            float originalHeight = originalImage.Height;

            Canvas canvas = new Canvas(resizedBitmap);

            float scale = this.Width / originalWidth;

            float xTranslation = 0.0f;
            float yTranslation = (this.Height - originalHeight * scale) / 2.0f;

            Matrix transformation = new Matrix();
            transformation.PostTranslate(xTranslation, yTranslation);
            transformation.PreScale(scale, scale);

            Paint paint = new Paint();
            paint.FilterBitmap = true;

            canvas.DrawBitmap(originalImage, transformation, paint);

            return resizedBitmap;
        }
    }
}

 

The Android ScrollView which is associated with the Xamarin Forms ScrollView has the following native properties:

  • VerticalScrollBarEnabled: Make the vertical scrollbar visible or hidden
  • HorizontalScrollBarEnabled: Make the horizontal scrollbar visible or hidden
  • OverScrollMode: Always enable the native bounce effect on Android ScrollView
  • Background: Allows to set the background drawable for the ScrollView

As you may have noticed we are converting our Xamarin Forms Image Source BackgroundImage to a Bitmap image using our extension.

Then we are resizing out Bitmap image according to the Width and Height of the ScrollView to fit to the full background to be wrapped around a BitmapDrawable and set to the Background of ScrollView.

There you go! 😀

Let’s use it… 😉

Alright now that’s done, let’s consume this in our PCL project.

<StackLayout Padding="10,0,10,0">

	<Label Text="Welcome to Xamarin Forms!"
		   VerticalOptions="Center"
		   HorizontalOptions="Center" />

	<local:BloopyScrollView 
	IsNativeBouncyEffectEnabled="True"
	IsVerticalScrollbarEnabled="False"
	IsHorizontalScrollbarEnabled="False">
	<local:BloopyScrollView.BackgroundImage>
	  <FileImageSource File="xamarinBackgroundImage.png"/>
	</local:BloopyScrollView.BackgroundImage>
	
			<Label
			  FontSize="22"
			  HeightRequest="400"
			  Text=
			  "Whatever your text content to be displayed." />
			  
	</local:BloopyScrollView>

</StackLayout>

 

As you can see I have inserted my BloopyScrollView in a StackLayout and as the content of the ScrollView I have added Label. Well you can add any content you want or set any Height or Width as you wish.

Notice that I have set IsNativeBouncyEffectEnabled to be True as I want to see the native Bouncy effect. Then I have disabled the Vertical and Horizontal Scrollbars from the properties we added earlier. Then finally I have added the BackgroundImage and set the FileImageSource to the ImageSource type, where as I have placed the image in the native Resource folder, as you would do with any defualt Xamarin Forms Image. 😉

Now let’s see the results… 😀

bloopscrollview-on-ios-lowq  bloopscrollview-on-android-lowq

Yaay! 😀

As we expected the Vertical and Horizontal Scrollbars are disabled and our ScrollView has full native bouncy effect accordingly.

Also you can see the Background Image nicely resized itself and fit to the background of the BloopyScrollView. 😀

Happy dance! lol

Recap Stuff…

Now there’s some stuff I wanted to recap, that is you may have noticed that when I was resizing the Image, I needed the Control’s Height and Width, and where I have acquired those properties are in two different places on each Android and iOS renderers.

To be specific I have accessed the Control’s Width and Height on Android right from the OnElementChanged method, but on iOS renderer I have accessed those values from the  OnPropertyChanged method’s Height property event. 

This is because of the differences of the Rendering cycling of Android and iOS, whereas on Android right at the firing of the Custom Renderer it assigns itself Width and Height. But on iOS we have to access them indirectly by waiting till those properties are set, by listening to the OnPropertyChanged event.

Get it on Github! 😀 XFImprovedScrollView

Cheers everyone!

Pass this on to another developer to make them smile! 😀
– Udara Alwis

Let’s resize a Bitmap and UIImage with Xamarin…

Since the beginning of computers, developers has been struggled with Images. So did I with Xamarin 😉

So here I am sharing my findings on resizing a Bitmap and UIImage respectively on Android and iOS, meanwhile preserving the aspect ratio. I’m sharing this for the ease of fellow Xamarin devs, if anyone is struggling to find a source to find solution for both Xamarin Android and iOS platforms.

Xamarin Android

Alright here goes resizing of a Bitmap on Xamarin Android, and please note that I merely convered this implementation from Java to C# when I was implementing it in my project, and here’s the reference for it : http://stackoverflow.com/a/8224161

You need to pass in the height and width you need to resize your Bitmap into. Also as you can see this resizing method scales up the Bitmap on the Y Axis, and scaling begins from the center of the Image. 🙂

private Bitmap ResizeBitmap(Bitmap originalImage, int widthToScae, int heightToScale)
{
	Bitmap resizedBitmap = Bitmap.CreateBitmap(widthToScae, heightToScale, Bitmap.Config.Argb8888);

	float originalWidth = originalImage.Width;
	float originalHeight = originalImage.Height;

	Canvas canvas = new Canvas(resizedBitmap);

	float scale = this.Width / originalWidth;

	float xTranslation = 0.0f;
	float yTranslation = (this.Height - originalHeight * scale) / 2.0f;

	Matrix transformation = new Matrix();
	transformation.PostTranslate(xTranslation, yTranslation);
	transformation.PreScale(scale, scale);

	Paint paint = new Paint();
	paint.FilterBitmap = true;

	canvas.DrawBitmap(originalImage, transformation, paint);

	return resizedBitmap;
}

 

Xamarin iOS

So below is what I used for UIImage on iOS, which I was lucky enough to find through the Xamarin Forum: https://forums.xamarin.com/discussion/comment/175585/#Comment_175585 So kudos to the original post! 🙂

public UIImage ResizeUIImage(UIImage sourceImage, float widthToScale, float heightToScale)
{
	var sourceSize = sourceImage.Size;
	var maxResizeFactor = Math.Max(widthToScale / sourceSize.Width, heightToScale / sourceSize.Height);
	if (maxResizeFactor > 1) return sourceImage;
	var width = maxResizeFactor * sourceSize.Width;
	var height = maxResizeFactor * sourceSize.Height;
	UIGraphics.BeginImageContext(new CGSize(width, height));
	sourceImage.Draw(new CGRect(0, 0, width, height));
	var resultImage = UIGraphics.GetImageFromCurrentImageContext();
	UIGraphics.EndImageContext();
	return resultImage;
}

 

Well there you have it.

Enjoy! 😀

An awesome Image Helper to convert Xamarin Forms ImageSource to iOS UIImage or Android Bitmap…

The default Xamarin Forms ImageSource is good, but it doesn’t provide all the properties of an Image, not as much as native Image types of Android or iOS. This is why sometimes we need to drill down to the native level of Image handling sometimes, specially when you’re dealing with Custom Renderers, or complex Image manipulation stuff in Xamarin.

So yeah it’s no surprise you will run into the need of converting the default Xamarin Forms ImageSource to native Image type in iOS and Android, respectively UIImage or Bitmap types.

Well I know I did. lol 😛

How ? 😮

So how could you do this ? Well, something intermediate for both Xamarin Forms ImageSource and the native Image types is the byte[] array. 🙂 But I’m gonna take a pass on it, since it’s too much of trouble and process, which could lead to bad memory consumption. 😦 Instead, why don’t we deal with this straight away. 😀

This is how I did it.. 😉

Now when it comes to Xamarin Forms almost everything is handled by drilling down to the native levels of the platform. Likewise ImageSource  during the runtime is handled through three types of Native Handlers that are as follows,

  • ImageLoaderSourceHandler
  • FileImageSourceHandler
  • StreamImagesourceHandler

Now for each Native environment, these handlers implements a LoadImageAsync() method, which loads the type of Native Type image for a given ImageSource.

This is usually done under the hood, but we need to access this same functionality on the go for our own requirements, so let’s do it by our own implementation.

Let’s create our Android Image Helper…

So we are going to create a Public class with static methods that could be used as extension methods in our Native Project levels. So go ahead and create the AndroidImageHelper class in your Xamarin.Android project level.

sameple

 

public class AndroidImageHelper
{
	private static IImageSourceHandler GetHandler(ImageSource source)
	{
		IImageSourceHandler returnValue = null;
		if (source is UriImageSource)
		{
			returnValue = new ImageLoaderSourceHandler();
		}
		else if (source is FileImageSource)
		{
			returnValue = new FileImageSourceHandler();
		}
		else if (source is StreamImageSource)
		{
			returnValue = new StreamImagesourceHandler();
		}
		return returnValue;
	}

	/// <summary>
	/// For converting Xamarin Forms ImageSource object to Native Image type
	/// </summary>
	/// <param name="source"></param>
	/// <param name="context"></param>
	/// <returns></returns>
	public static async Task<Bitmap> GetBitmapFromImageSourceAsync(ImageSource source, Context context)
	{
		var handler = GetHandler(source);
		var returnValue = (Bitmap)null;

		returnValue = await handler.LoadImageAsync(source, context);

		return returnValue;
	}
}

 

Alright there we go, as you would have expected we are using the native level Handlers of the ImageSource and retrieving the native image type as I explained earlier through the LoadImageAsync() method. Of course you need to pass a reference of your current Context since Android requires the context reference to almost every execution related to the UI stuff.

First we are getting the GetHandler type by the ImageSource, then we are calling the method above to retrieve the Bitmap image and returns back to the caller.

Let’s create our iOS Image Helper…

So just like on Android let’s do the same on iOS and create the public class IosImageHelper in your Xamarin Forms iOS project level.

sameple

public class IosImageHelper
{
	private static IImageSourceHandler GetHandler(ImageSource source)
	{
		IImageSourceHandler returnValue = null;
		if (source is UriImageSource)
		{
			returnValue = new ImageLoaderSourceHandler();
		}
		else if (source is FileImageSource)
		{
			returnValue = new FileImageSourceHandler();
		}
		else if (source is StreamImageSource)
		{
			returnValue = new StreamImagesourceHandler();
		}
		return returnValue;
	}

	/// <summary>
	/// For converting Xamarin Forms ImageSource object to Native Image type
	/// </summary>
	/// <param name="source"></param>
	/// <returns></returns>
	public static async Task<UIImage> GetUIImageFromImageSourceAsync(ImageSource source)
	{
		var handler = GetHandler(source);
		var returnValue = (UIImage)null;

		returnValue = await handler.LoadImageAsync(source);

		return returnValue;
	}

}

 

So here also we are using the same implementation as we used on Android, instead the LoadImageAsync() returns an UIImage.

Now let’s use it… 😉

Alright let’s see how to use these extensions in our code. 🙂

// Useage in iOS

UIImage _uiImageconverted = await IosImageHelper.GetUIImageFromImageSourceAsync(yourImageSourceObject);

// Useage in Android

Bitmap _bitmapImageconverted = await AndroidImageHelper.GetBitmapFromImageSourceAsync(yourImageSourceObject, this.Context);

 

There you have it, now you have your Xamarin Forms ImageSource converted to the given Native Image type, either iOS UIImage or Android Bitmap Image type. 😀

Enjoy! 😀

Cheers everyone!